JPH08213664A - Multilayered ceramics piezoelectric element - Google Patents

Abstract

PURPOSE: To provide a multilayered ceramic piezoelectric element wherein the resonance frequency difference of each phase is small and energy loss is little when the element is used in a Langevin type ultrasonic motor, by forming the upper surface and the lower surface of the element except surface electrodes, in planes wherein the difference of unevenness is smaller than or equal to a specific value. CONSTITUTION: A PZT system piezoelectric sheet is used, an inner electrode is formed by a printing method, and a multilayered ceramic piezoelectric element 1 in which 15 layers are laminated is formed. After insulator is stuck on the side surfaces of the respective piezoelectric sheets every other layers, interlayer wirings 3 are connected by using conductive paste, and then baked. The upper surface and the lower surface of the element are formed in flat planes wherein the difference of unevenness in each surface is at most 20μm. Surface electrodes 4 connected with the interlayer wirings 3 are formed on the flat upper surface of the element by a sputtering method. Every four forming positions of the surface electrodes 4 are collectively constituted in the front part and the rear part of the upper surface of the element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated ceramics piezoelectric element suitable for, for example, a Langevin type ultrasonic motor, and more specifically, when it is driven by using high-frequency signals of two or more phases different in phase from each other. The present invention relates to a laminated ceramic piezoelectric element having a small difference in phase resonance frequency and a small energy loss.

[0002]

2. Description of the Related Art Conventionally, as a vibrating element used in, for example, a Langevin type ultrasonic motor, Japanese Patent Laid-Open No. 3-407 is known.
No. 67, JP-A-3-117384, etc., a plurality of single piezoelectric element plates whose polarization directions in the thickness direction are reversed left and right or front and back are overlapped with an electrode plate sandwiched therebetween. The one having the different structure is used (see FIG. 8).
However, in recent years, attempts have been made to reduce the drive voltage and downsize the element by using a so-called laminated ceramics piezoelectric element that integrates this structure.

Here, the laminated ceramics piezoelectric element 10 is used.
1, there is an internal electrode 102 having an electrode pattern formed such that a ring is divided into four, for example, as shown in FIG. 7, for each interlayer, and the internal electrodes 102 are provided every other layer in the stacking direction.
03, and the surface electrode 104 is connected to the interlayer wiring 103 on the surface. Then, in this element 101, for example, when a positive voltage is applied, the thickness increases in the first quadrant and the second quadrant, and the thickness decreases in the third quadrant and the fourth quadrant (of course, when a negative voltage is applied. Is
Each quadrant behaves in the opposite way). When driving the element 101, the first
Resonant frequency signals of the same phase are input to the quadrant and the third quadrant (hereinafter, "A phase"), and the phase is relative to the signal in the second quadrant and the fourth quadrant (hereinafter, "B phase"). By inputting a resonance frequency signal that is shifted by 90 degrees, the vibration of the neck is caused.

The above-mentioned laminated ceramics piezoelectric element is
The thickness of each layer that makes up the device is sufficiently smaller than the thickness of a single-plate device, and since it can be multi-layered, the voltage required for driving can be greatly reduced, and the device can be made smaller and driven at lower voltage. This is an element having many excellent characteristics such as being capable of being achieved.

[0005]

However, here,
When a Langevin type ultrasonic motor or actuator is actually manufactured using the above-mentioned laminated ceramics piezoelectric element, the difference (ΔF) in resonance frequency between the A phase and the B phase of the vibrator is large, and The quality factor (Qm) was also inferior to the case of using a single-plate element, and a motor or actuator sufficient for practical use could not be obtained.

The present invention has been made in view of the problems when the above-mentioned laminated ceramics piezoelectric element is used in a Langevin type ultrasonic motor or actuator, and its object is to provide a Langevin type ultrasonic motor or Another object of the present invention is to provide a laminated ceramics piezoelectric element having a small difference in resonance frequency of each phase and a small energy loss even when used for an actuator, and further to provide a method for supplying power to the element.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned objects, the present inventors have found that when a laminated ceramic piezoelectric element is used in a Langevin type ultrasonic motor or actuator, The inventors have found that it is the smoothness of the upper and lower surfaces of the device that affects the difference (ΔF) in the resonance frequency of the phases and the mechanical quality factor (Qm), and completed the present invention.

That is, according to the present invention, in a laminated ceramics piezoelectric element used in a Langevin type ultrasonic motor or actuator, the upper and lower surfaces of the element excluding the surface electrodes have a difference in unevenness of 20 μm or less within the surface. The laminated ceramics piezoelectric element formed on the plane of Further, the present invention, the area of each of the above surface electrode, 0.002mm ² or more 0.2
The laminated ceramic piezoelectric element was formed to have a surface area of ² mm ² or less and each of the surface electrodes protruding from the element surface. Furthermore, the present invention provides a laminated ceramics piezoelectric element in which the protrusion amount of each of the surface electrodes is 1 μm or more and 20 μm or less. Further, the present invention provides a laminated ceramics piezoelectric element in which the surface electrodes are arranged in a well-balanced manner within the surface of the element. Furthermore, the present invention provides a laminated ceramic piezoelectric element in which electrodes existing inside the element are connected by interlayer wiring formed inside the element. Furthermore, according to the present invention, a wiring board is used as a method for supplying power to the above-mentioned laminated ceramics piezoelectric element. Hereinafter, each of the above-described present inventions will be described in more detail.

First, in the present invention, regarding the smoothness of the upper and lower surfaces of the element, it is specified that the unevenness in the surface is formed on a flat surface of 20 μm or less. This means that when the difference between the unevenness in the upper and lower surfaces of the element is larger than 20 μm, when used in a Langevin type ultrasonic motor or actuator,
This is because the test revealed that the mechanical quality factor (Qm) as a whole was lowered and the difference (ΔF) in resonance frequency between the phases was also increased.

There are roughly two methods for producing a laminated ceramics piezoelectric element having such smooth upper and lower surfaces. One is a method of manufacturing an element having high flatness by performing warp correction (re-baking) or processing (lap) after firing, and in this case, the surface electrode and the like may be formed after that. . The other is a method of manufacturing while carefully controlling steps such as molding and firing so that deformation or warpage does not occur. In the present invention, any of the methods described above may be used, and the method for making the method is not particularly limited.

In the present invention described above, the height of the surface electrode is not taken into consideration. Therefore, when the device of the present invention is used, the terminal should be arranged so as to cancel the height of the surface electrode. There is a need to. Specifically, it is necessary to take a measure such as denting the terminal portion of the electrode plate connected to the surface electrode by the height of the electrode.

Further, when measuring the difference in unevenness (excluding the surface electrode portion) in the upper and lower surfaces of the element, the element is placed on a plane and three-dimensionally measured by a non-contact type shape measuring device or the like. Is preferable because the value can be measured accurately. This can be measured with a contact-type shape measuring device, for example, a surface roughness meter, but if the back surface of the element is convex, for example, the element will move easily due to needle pressure, etc. This is because it becomes difficult to perform accurate measurements.

[0013] Next, in the present invention, in addition to the above requirements, the individual surface electrode with a 0.002 mm ² or more 0.2 mm ² or less of the area, forming each of the surface electrodes protrude from the element surface Is prescribed. This is because if an element having such a surface electrode can be connected to the surface electrode by using an electrode plate, it becomes an element having a smaller resonance frequency difference (ΔF) and a mechanical quality factor (Qm). ) Is also high. That is, when the area of the surface electrode is smaller than 0.002 mm ² , the resistance value of the connecting portion becomes large and the mechanical quality factor (Qm) is lowered, and when the area is larger than 0.2 mm ² , a flexible substrate is used. This is because it was found by a test that the influence of the electrode thickness or the amount of protrusion thereof cannot be eliminated, and the difference (ΔF) in the resonance frequency between the phases becomes large. Further, it is desirable that the surface electrode protrudes from the element surface in order to ensure connection with the electrode plate.

As a method for forming the surface electrode as described above, the printing method is the simplest, but is not limited to this forming method, and for example, a CVD method, a sputtering method, or the like may be used. It is also possible to form a conductor layer on the entire surface of, and then to dig into the periphery by etching or the like to form the surface electrode.

When the numerical value that defines the area of the surface electrode is converted into a circular diameter, it is approximately 50 μm or more and 500 μm or more.
Although the surface electrode has the following diameter, the surface electrode does not need to be circular, and is defined by the area in the present invention. Further, the area of the surface electrode defined in the present invention,
It is the projected area when viewed from the top surface, and the height component due to the protrusion is not taken into consideration.

Next, in the present invention, regarding the amount of protrusion of the surface electrode which is the above requirement, the amount of protrusion of each surface electrode is set to 1
It is specified that the thickness is not less than μm and not more than 20 μm. This is a laminated ceramics piezoelectric element that is practically sufficient even with the above requirements alone, but if the amount of protrusion of the surface electrode from the element surface is within the above range, the difference in resonance frequency between each phase This is because tests have revealed that the element has a small (ΔF) and a high mechanical quality factor (Qm), and the element is surely conducted and has higher reliability.

There is no particular limitation on the method of forming the surface electrode having the above-mentioned protrusion amount, but the printing method is most suitable in view of the protrusion amount (thickness) of the surface electrode to be formed. Further, the laminated ceramics piezoelectric element 11 shown in FIG. 5 described later, that is, the electrode 12 existing inside the element
In the element in which the spaces are connected by the inter-layer wiring 13 formed inside the element, when the surface lapping of the element 11 is performed, the piezoelectric material base is formed more than the inter-layer wiring 13 (usually formed of Ag-Pd or Pt). Since the (generally made of PZT-based ceramics) is better shaved and, as a result, the inter-layer wiring 13 projects from the element surface, the surface electrode having the above-mentioned projection amount is controlled by controlling the lapping conditions. It is also possible to form 14.

Next, in the present invention, regarding the positional relationship of the surface electrodes formed on the element, it is specified that the surface electrodes are arranged in a well-balanced manner within the surface of the element. This is a noise for resonance because the surface electrode itself does not vibrate even if the influence of the surface electrode thickness or the amount of protrusion thereof can be eliminated by using a flexible substrate.
If such surface electrodes are formed concentratedly in one place of the element, a difference in resonance frequency naturally occurs between the element part where the surface electrode is concentrated and another element part, and as a result, the mechanical frequency is increased. This is because the quality factor (Qm) also decreases.

The term "distribute the surface electrodes in a well-balanced manner in the plane of the device" as used herein means not only the case where eight surface electrodes are arranged at equal intervals on the same circumference, but also two surface electrodes are arranged at a time. The case where the approaching surface electrodes are arranged at equal intervals at four places on the same circumference is also included.

Next, the present invention defines that the internal electrodes 12 of the element 11 are connected by the interlayer wiring 13 formed inside the element as shown in FIG. This is because by forming the interlayer wiring 13 inside the element, it is possible to eliminate the interlayer wiring (for example, the interlayer wiring 103 shown in FIG. 7) that gives an extra protrusion to the outer peripheral wall surface of the element. This is because noise due to resonance can be removed, the resonance frequency difference between the vibrators is further reduced, and the resonance curve is sharpened to increase the mechanical quality factor (Qm).

The inter-layer wiring 13 inside the element is a so-called via hole or through hole.
It can be formed by using a low temperature firing type ceramics substrate manufacturing technique. The general method of making via holes is to make a hole in the green sheet of the piezoelectric body before lamination, fill the hole with a conductor paste, print the internal electrode pattern on it, and then laminate and fire. Is. By doing so, the internal electrodes and the via-hole electrodes are integrally fired, and the wiring connecting the layers of the element can be formed. Of course, a method other than the above may be used as long as an interlayer wiring can be formed inside the element.

Further, in the present invention, as shown in FIG. 6, as a method for supplying power to the element A according to the present invention, it is prescribed that the wiring board B is pressed against the surface of the element A having the surface electrode. . This is because a conductive layer is formed on the wiring board B. For example, when the element A according to the present invention is used in a Langevin type ultrasonic motor as shown in FIG. 6, a bolt C and a stator D ₁ are used. , biting surface electrodes projecting from the surface of the element a to the conductive layer of the wiring board B by the fastening force by the D _2, together with the continuity is ensured, the surface electrode and the conductor layer occurs plastic deformation, contact This is because it is possible to make uniform.

Here, as the wiring board B, a conductor such as copper or solder is electrically conductive on the surface of a board made of an insulating material such as a polymer material having high elasticity and / or plasticity. So-called flexible substrates formed as body layers are preferred. This is because the wiring board B having such a property is easily deformed by the tightening force of the bolt C and the stators D ₁ and D ₂ to further reduce the influence of the surface electrode protruding from the surface of the element A. This is because the element A is uniformly contacted.

The conductor layer on the wiring board B has wirings made of a conductor on almost the entire surface thereof in order to separately supply power and conduct electricity to each surface electrode of the laminated ceramics piezoelectric element A.

[0025]

In the Langevin type ultrasonic motor of the type in which a plurality of conventional single-plate piezoelectric element plates are used,
For example, between the ceramic piezoelectric element plate a ₁ ~a ₅ in the five shown in FIG. 8, six metal plates b ₁ ~b as electrode
_A vibrator is formed by sandwiching ₆ and metal plates b ₁ to b are attached to the vibrator.
_A drive signal is input via ₆ , and these six metal plates b _{1 to} b ₆ are used as ceramics piezoelectric element plates a _{1 to} a _{5 respectively.}
Absorbs irregularities on the upper and lower surfaces of the bolt c and the stators d ₁ , d
_The tightening force due to ₂ and each ceramic piezoelectric element plate a ₁
~ A ₅ works evenly on the plate surface, and the difference in resonance frequency of each phase (Δ
It is considered that the ultrasonic motor had a small F) and a high mechanical quality factor (Qm). Needless to say, the efficiency as a motor was not good due to the vibration absorbing action of the large number of metal plates b _{1 to} b ₆ sandwiched between these ceramics piezoelectric element plates.

However, in the case of the laminated ceramics piezoelectric element, since the electrode is already formed inside the element, the surface plate of the element A is used as the electrode plate as shown in FIG. 6, for example. Although only one electrode plate B is required for conduction, theoretically the efficiency should be improved. However, when the element is tightened by the bolt and the stator, the absorption is absorbed in the conventional single-plate piezoelectric element plate. The concavities and convexities existing on the upper and lower surfaces of the element, which were already present, become noticeable, and the tightening force between the bolt and the stator becomes uneven within the plate surface of the element, which in turn reduces the efficiency of the motor and the resonance of each phase. It is considered to cause an increase in frequency difference.

Therefore, in the present invention, the laminated ceramics piezoelectric element is of the Langevin type by defining in detail the smoothness of the upper and lower surfaces of the laminated ceramics piezoelectric element, the area of the surface electrode, the protruding amount thereof, and the like. When used in an ultrasonic motor or actuator, the tightening force of the bolt and the stator acts uniformly on the plate surface of the element, and the multilayer ceramic piezoelectric element has the original characteristics and practically sufficient performance. It was possible to provide an ultrasonic motor or actuator having the same.

[0028]

[Test Example] A test example for demonstrating the effect of the above-described laminated ceramic piezoelectric element according to the present invention will be described below.

-Test 1- Using a PZT type piezoelectric sheet, an internal electrode 2 was formed by a printing method to prepare a laminated ceramics piezoelectric element 1 having a structure as shown in FIG. This element 1 has a thickness of about 100 μm per layer, and a total of 15 layers are laminated to form an element having a diameter of 10 mm and an inner diameter of 5 mm. Interlayer wiring 3
Is formed by applying an insulator every other layer on the side surface of each piezoelectric sheet during the manufacturing thereof, connecting them using a conductor paste, and then firing. The upper and lower surfaces of the element are formed into a smooth flat surface having a difference in irregularities (hereinafter referred to as “flatness”) of 1 to 20 μm in each of the upper and lower surfaces by lapping after firing. A surface electrode 4 connected to the interlayer wiring 3 on the side surface is formed on the upper surface by sputtering to have a thickness of 1 μm. The number of the surface electrodes 4 is eight in total, that is, four positions of + and − for each of the A phase and the B phase, and four positions of each ground, and the formation position thereof is on the upper surface of the element as shown in FIG. Four pieces are formed in each of the front part and the rear part. After the above-mentioned several laminated ceramics piezoelectric elements were polarized, they were incorporated into a Langevin type ultrasonic motor as shown in FIG. 6, and the mechanical quality factor (Qm) was measured and found to be 500 to 700. Further, the difference (ΔF) in resonance frequency between the A phase and the B phase was 70 to 100 Hz.

-Test 2- The same structure as in Test 1 was applied to several laminated ceramic piezoelectric elements having flatness of 24 to 40 μm without lapping the upper and lower surfaces of the element after firing in Test 1 described above. When the mechanical quality factor (Qm) when the element was incorporated in the Langevin type ultrasonic motor and the difference (ΔF) in the resonance frequency between the A phase and the B phase were measured under the following conditions,
The m value was 200 to 450 and the ΔF value was 110 to 230 Hz. It should be noted that the quality is judged by Qm in view of the motor performance.
Since the value is 500 or more and the ΔF value is 110 Hz or less,
The results of test 2 are not favorable.

-Test 3-For an element (flatness 15 μm) manufactured in the same manner as in Test 1, the surface electrodes were formed by a printing method so that the area of each surface electrode 4 was a value shown on the horizontal axis of FIG. Other than that, the mechanical quality factor (Qm) and the resonance frequency difference (ΔF) between the A-phase and the B-phase were measured when assembled in a Langevin type ultrasonic motor under the same structure and conditions as in Test 1. did. Figure 2
Shows the relationship between the measured Qm and ΔF and the surface electrode area.

-Test 4-For an element (flatness 15 μm) manufactured in the same manner as in Test 1, the area of each surface electrode 4 was 0.02 mm ² by the printing method, and the amount of protrusion of each surface electrode 4 was A surface electrode was formed so as to have a value shown on the horizontal axis of FIG. 3, and the mechanical quality factor (Qm) when the surface electrode was incorporated into a Langevin type ultrasonic motor under the same structure and conditions as in Test 1 and other conditions, and Phase A and B
The difference (ΔF) in resonance frequency from the phase was measured. FIG.
Shows the relationship between the measured Qm and ΔF and the protrusion amount of the surface electrode.

-Test 5-For the element (flatness 15 μm) manufactured in the same manner as in Test 1, the formation position of the surface electrode 4 (area 0.02 mm ² , protrusion amount 5 to 10 μm) was measured as shown in FIG. A mechanical quality factor (Qm) when the element was incorporated in a Langevin type ultrasonic motor under the same structure and conditions as in Test 1 except that the elements were arranged on the upper surface at equal intervals, and A phase and B phase. When the difference in resonance frequency (ΔF) was measured, the Qm value was 830 and the ΔF value was 57 Hz. This result indicates that the formation position of the surface electrode has an effect on improving the Qm value and the ΔF value.

-Test 6- A piezoelectric sheet formed of the same material as the piezoelectric sheet used in Test 1 was used to punch the piezoelectric sheet with a diameter of 15
Open a 0 μm hole (via hole) and put Ag-Pd in the hole.
After being filled with the conductive paste, the pattern of the internal electrodes was printed, and then the sheets were laminated and baked as shown in FIG. 5 to fabricate an element having the internal electrodes 12 and the interlayer wiring 13. Next, after wrapping the upper and lower surfaces of the above element so as to have the flatness shown in Table 1, an A type element in which the surface electrode 14 having the area and the protruding amount shown in Table 1 was newly formed by a printing method, A B-type element in which the via electrode protruding from the surface of the element by lapping was used as it was as the surface electrode 14 having the area and the protruding amount shown in Table 1 was manufactured, and each of the laminated ceramic piezoelectric element 11 was polarized. After that, it was incorporated into a Langevin type ultrasonic motor, and its mechanical quality factor (Qm) and the resonance frequency difference (ΔF) between the A phase and the B phase were measured. The measurement results are shown in Table 1.

[0035]

[Table 1]

From Table 1, any element having a flatness of the device of 20 μm or less, an area of the surface electrode of 0.2 mm ² or less, and a protruding amount of the surface electrode of 20 μm or less should show good performance as a vibrator. Turns out.

According to each of the above-mentioned test examples, when the laminated ceramics piezoelectric element according to the present invention is incorporated in a vibrator of a Langevin type ultrasonic motor, the difference (ΔF) in resonance frequency between the respective phases is small, Moreover, the mechanical quality factor (Q
It turns out that m) is a high element. Further, it is found that the laminated ceramics piezoelectric element according to the present invention can be sufficiently applied as a laminated ceramics piezoelectric element for an annular ultrasonic motor.

[0038]

As described above, according to the laminated ceramics piezoelectric element according to the present invention described above, it is possible to provide an ultrasonic motor or actuator having the characteristics peculiar to the laminated ceramics piezoelectric element and having practically sufficient performance. Is possible.

[Brief description of drawings]

FIG. 1 is a conceptual structural view and an external view of a laminated ceramics piezoelectric element according to the present invention.

FIG. 2 is a diagram showing the relationship between Qm, ΔF and the surface electrode area in Test 3.

FIG. 3 is a diagram showing a relationship between Qm and ΔF and a protrusion amount of a surface electrode in Test 4.

FIG. 4 is a conceptual structural view and external view of a laminated ceramics piezoelectric element according to the present invention.

5A and 5B are a conceptual structural view and an external view of a laminated ceramics piezoelectric element according to the present invention.

FIG. 6 is a conceptual cross-sectional view of an ultrasonic motor incorporating a laminated ceramics piezoelectric element according to the present invention.

FIG. 7 is a conceptual structural view and an external view of a laminated ceramics piezoelectric element.

FIG. 8 is a conceptual sectional view of an ultrasonic motor incorporating a plurality of conventional ceramics piezoelectric element plates.

[Explanation of symbols]

 1,11 Multilayer Ceramics Piezoelectric Element 2,12 Internal Electrode 3,13 Interlayer Wiring 4,14 Surface Electrode B Wiring Board

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yutaka Maruyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Nobuyuki Kojima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Within the corporation

Claims (8)

[Claims] 1. The upper and lower surfaces of a part of the device excluding the surface electrodes are:
A laminated ceramics piezoelectric element, characterized in that the difference in the in-plane unevenness is formed on a flat surface of 20 μm or less. 2. The area of each surface electrode is 0.002 mm ²
And 0.2 mm ² or less, and each of the surface electrodes is
2. The laminated ceramics piezoelectric element according to claim 1, wherein the laminated ceramics piezoelectric element is formed so as to project from the element surface. 3. The protrusion amount of each of the surface electrodes is 1 μm.
3. The laminated ceramic piezoelectric element according to claim 2, wherein the thickness is 20 μm or less. 4. The multilayer ceramic piezoelectric element according to claim 1, 2 or 3, wherein the surface electrodes are arranged in a well-balanced manner in the plane of the element. 5. The laminated ceramics piezoelectric element according to claim 1, wherein the electrodes existing inside the element are connected by an interlayer wiring formed inside the element. Body element. 6. The wiring board is pressed against the surface of the element having the surface electrode, and power is supplied to the element through the wiring board, according to claim 1, 2, 3, 4 or 5. Multilayer ceramic piezoelectric element. 7. The laminated ceramics piezoelectric element according to claim 6, wherein the wiring board is a flexible board. 8. The laminated ceramic piezoelectric element according to claim 1, wherein the element is used in an ultrasonic motor.